CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

Flat epsilon residuals

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   April 22, 2015, 07:44
Default Flat epsilon residuals
  #1
New Member
 
Join Date: Jul 2012
Location: France
Posts: 26
Rep Power: 6
pipolaki is on a distinguished road
Hello,

I currently have a problem with my DPM simulation on ANSYS Fluent V15. Epsilon residuals are stuck around 1.0 during the computation (Image here :
https://drive.google.com/folder/d/0ByiqwBpvr2T0VXR2VkJhYVl3elE/edit ).
As soon as I uncheck the 2-way turbulence coupling option, the epsilon residual is decreasing.
Is there any explanation about this ?
Is it normal to have convergence issues concerning epsilon ?
According you, can I trust the results of my simulation with such high epsilon residuals ?

Thank you for your help.

Last edited by pipolaki; April 27, 2015 at 06:54.
pipolaki is offline   Reply With Quote

Old   June 1, 2015, 08:19
Default
  #2
New Member
 
Join Date: Jul 2012
Location: France
Posts: 26
Rep Power: 6
pipolaki is on a distinguished road
I'm still wondering why the epsilon residual remains flat when 2-way turbulence coupling is active... Any ideas ?
pipolaki is offline   Reply With Quote

Old   February 10, 2017, 03:47
Default
  #3
New Member
 
Outside US and Canada
Join Date: Apr 2015
Posts: 6
Rep Power: 4
arctan is on a distinguished road
I've got the same problem, epsilon residual flat around 1.0. Have you worked it out?
arctan is offline   Reply With Quote

Old   February 10, 2017, 10:57
Default
  #4
New Member
 
Join Date: Jul 2012
Location: France
Posts: 26
Rep Power: 6
pipolaki is on a distinguished road
I completely forgot this topic : thank you for your question.

In order to avoid the epsilon residual problem, Ansys support suggested me to use a first order discretization scheme for turbulence and it worked : no more issues on epsilon residuals.

Moreover, I found that in my study the option "two-way turbulence coupling" was improving my results when I compared them with our experimental datas.

Please, let me know if this solution is helping you or not.

Regards.

Quote:
Originally Posted by arctan View Post
I've got the same problem, epsilon residual flat around 1.0. Have you worked it out?
pipolaki is offline   Reply With Quote

Old   February 12, 2017, 23:18
Default
  #5
New Member
 
Outside US and Canada
Join Date: Apr 2015
Posts: 6
Rep Power: 4
arctan is on a distinguished road
Hi Pipolaki,
Thanks for your reply!
I tried to switch to first order discretization scheme for turbulence, unfortunately, it wouldn't work for me. Then I tried a smaller under-relaxation factor for turbulent epsilon and the epsilon residual did decrease by an order of magnitude, but it remained there. As I unchecked the two-way turbulence coupling, the epsilon was decreasing.
Is it normal to have convergence issues concerning epsilon, with two-way turbulence coupling option ?
Can I trust the results of my simulation with such high epsilon residuals ?
Regards,
arctan is offline   Reply With Quote

Old   February 17, 2017, 04:21
Default
  #6
New Member
 
Join Date: Jul 2012
Location: France
Posts: 26
Rep Power: 6
pipolaki is on a distinguished road
Sorry to hear that the first order scheme didn't work for you. I have no other suggestion.

I also noticed that if the two-way turbulence coupling was unchecked, the epsilon residual decreased and this behavior is still mysterious to me.

My personal opinion (which is not very valuable !) is that if the residual is high, it's not good for your results. If I were you, I would perform two computations :
- one with the 2-way turbulence coupling checked and its high epsilon residual ;
- another with the 2-way turbulence coupling unchecked and all the good residuals.
Then I would compare the results, especially those which concerns the turbulence properties. Maybe it could help you to choose between the two solutions.

Good luck.
pipolaki is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
SimpleFoam k and epsilon bounded nedved OpenFOAM Running, Solving & CFD 16 March 4, 2017 09:30
Flat residuals dreamz Main CFD Forum 0 March 3, 2014 07:16
epsilon and K blowing up. sivakumar OpenFOAM Running, Solving & CFD 1 October 25, 2012 04:50
k and epsilon residuals not converging NISHIKANT TAMRAKAR FLUENT 9 October 11, 2011 10:47
SimpleFoam k and epsilon bounded nedved OpenFOAM Running, Solving & CFD 1 November 25, 2008 21:21


All times are GMT -4. The time now is 06:00.